Inversion season is here. What you’re supposed to avoid doing

Residents warned to avoid outdoor exercise, refrain from woodburning and reduce driving.

(Francisco Kjolseth | The Salt Lake Tribune) Winter inversion conditions settle into the Salt Lake Valley obscuring the landscape on Monday, Dec. 7, 2020. Forecasters say the problem is expected to worsen until Friday, when unsettled weather should blow away the gunk.

Look out, Utah’s dreaded inversion season is back.

With the arrival of winter’s first prolonged pollution-trapping weather event, Utah environmental regulators have imposed mandatory actions this week, calling on Wasatch Front residents to minimize driving, refrain from burning wood and take other steps to limit the emissions now filling the valleys.

Levels of fine particulate, or PM2.5, have spiked toward the public health limit set by the federal government in Salt Lake and Davis counties. The Utah Division of Air Quality is forecasting worsening conditions through Friday, when unsettled weather is expected to bring snow and rain and push out pollution.

“We’ve been there already for a little less than a week. The numbers haven’t climbed too high because it’s a weak, high inversion. It goes up and down as the days go by. There’s enough space for some to blow out,” said Bo Call, the division’s monitoring supervisor.

Particulate-forming emissions come mostly from vehicles, but homes, industrial sites and agriculture are also big contributors.

In wintertime inversions, when calm weather persists over the valleys and air flow stagnates, warmer air sitting above presses down on cooler air, concentrating PM2.5 in low-lying areas. The PM2.5 readings peaked Monday afternoon at 35 micrograms per cubic meter in Salt Lake City, 43 in Utah County and 52 in Davis County, according to state monitoring data.

When the air gets gunky, public health officials warn people to avoid exercising outdoors in lower-elevation areas. People with preexisting health conditions should stay indoors. Conditions tend to be worse when it’s colder and snow covers the ground, according to Call. Warming raises the ceiling of the inversion, which reduces the concentration of pollution and allows it to blow around.

Fine particulate is linked to numerous diseases and contributes to 45,000 premature deaths each year, according to the Environmental Protection Agency, or EPA.

Public health advocates have called for tightening the federal standard, currently set at 35 micrograms averaged over 24 hours.

The outgoing Trump administration on Monday, however, declined to lower that threshold, despite growing evidence indicating a connection between this pollution and coronavirus death rates.

“This is yet another careless act by the Trump administration that disregards public health and well-being,” said Joro Walker, Salt Lake City-based general counsel at Western Resource Advocates. “It’s reckless not to tighten this standard as Western communities grapple with air choked by wildfire smoke, pollutants such as ozone are increasing, and COVID-19 infections continue to rise and attack the lungs.”

Last spring, however, EPA Administrator Andrew Wheeler proposed keeping the standard in place, saying there was insufficient scientific evidence to warrant making it more stringent.

“The United States is a world leader in growing our economy while simultaneously improving air quality,” said Utah Rep. Rob Bishop at the time. “Between 1970 to 2018, air pollutants identified in the Clean Air Act have fallen 74% while the U.S. economy has grown by 275%. EPA’s decision to maintain the current National Particulate Matter Standards reflects this fact. Administrator Wheeler and the administration should be commended for partnering with states, local, and tribal governments in improving our air quality while allowing economic growth to continue.”

Walker called on the incoming Biden administration to reverse Wheeler’s decision.

“By tightening the federal standard for particulate matter pollution, the EPA could protect our health and environment, and prevent thousands of premature deaths annually,” she said. “This is especially important for protecting communities of color and low-income communities, which are disproportionately harmed by particulate matter pollution due to decades of environmentally racist policies.”

Lowering the standard to 30 micrograms, could prevent 540 premature deaths a year, according to EPA’s own assessment.

For years, Salt Lake County’s air quality has been out of attainment of federal standards set for particulate matter and ozone. The EPA recently announced Wasatch Front air quality had improved enough to officially redesignate its air as in compliance with the PM2.5 standard, although summertime ozone pollution remains a serious problem.